Showing papers on "Stress relaxation published in 1969"
TL;DR: The morphology of solution cast films of butadiene and styrene block polymers in both stretched and unstretched state has been studied by electron microscopy, and has been related to the mechanical behavior of these materials as mentioned in this paper.
Abstract: The morphology of solution cast films of butadiene and styrene block polymers in both stretched and unstretched state has been studied by electron microscopy, and has been related to the mechanical behavior of these materials. These micrographs confirm the indications from dynamic properties that this material consists of a two-phase system in which the relationship between the phases is sensitive to the solvent system used in casting. Although the basic morphological unit is a polystyrene sphere of 100 A diameter dispersed in a matrix of polybutadiene, the interaction between spheres is complex. These spheres are more deformable than would be predicted from their glass transition temperature. The dynamic mechanical properties, stress-strain properties, and stress relaxation properties of block polymers of styrene and dienes can be explained in terms of the morphology and changes of morphology on stretching in the electron microscope.
82 citations
TL;DR: In this article, a model for the non-Newtonian viscous behavior of polymer melts has been proposed; it is based on the mol. wt. distribution and an approximation to the behaviour of a monodisperse polymer.
69 citations
TL;DR: The applicability of the following strain rate equation to high temperature deformation is examined in this paper, where it is shown that, as long as σ and v are independent of instantaneous changes in applied stress and temperature, a back stress term must be included if the equation is to be valid for transient as well as steady-state conditions.
69 citations
IBM1
TL;DR: The authors of as discussed by the authors showed that the stress required to operate dislocation sources within a grain, at a grain boundary, and at surfaces is larger than the intrinsics tresses observed in polycrystalline films.
Abstract: The stress required to operate dislocation sources within a grain, at a grain boundary, and at surfaces is found to be larger than the intrinsics tresses observed in polycrystalline films. It is therefore unlikely that a dislocation flow mechanism can relieve stresses in films. Grain boundary sliding and diffusional creep can, however, relieve stresses in films and equations describing the kinetics of stress relaxation are derived. It is suggested that stress relief occurs primarily by a diffusion-creep mechanism. Growth of hillocks during annealing of a film is briefly discussed in terms of the diffusion-creep mechanism.
65 citations
01 Dec 1969
TL;DR: In this paper, the authors report that under different states of stress, CREEP is SOMEWHAT SMALLER THAN under UNIAXIAL STRESS, while under multiaxial STRESS CREEP'S RATIO is LOWER.
Abstract: CREEP DATA ARE PRESENTED FOR CONCRETE UNDER DIFFERENT STATES OF STRESS, WITH EACH STRESS COMPONENT INDEPENDENTLY CONTROLLED. CREEP IN ALL THREE PRINCIPAL DIRECTIONS IS REPORTED. UNDER MULTIAXIAL STRESS, CREEP IS SOMEWHAT SMALLER THAN UNDER UNIAXIAL STRESS. EFFECTIVE CREEP POISSON'S RATIO UNDER MULTIAXIAL STRESS IS LOWER (0.09 TO 0.17) THAN UNIAXIAL CREEP POISSON'S RATIO (0.17 TO 0.20) AND DEPENDS ON THE RELATIVE MAGNITUDE OF PRINCIPAL STRESSES. EMPIRICAL EXPRESSIONS FOR CREEP POISSON'S RATIO ARE DERIVED. DATA ON CREEP RECOVERY SHOW THE DEPENDENCE OF CREEP RECOVERY ON PRECEDING CREEP AS WELL AS ON STRESS REMOVED. UNDER MULTIAXIAL COMPRESSION THE RECOVERABLE PROPORTION OF CREEP IS LARGER THAN UNDER UNIAXIAL STRESS. /AUTHOR/
62 citations
TL;DR: In this article, a logarithmic stress relaxation was studied in 99.999% polycrystalline nickel at natural strains of up to 25% at 20, 77, 200 and 293°K.
34 citations
TL;DR: In this paper, a theoretical analysis is made of the dimensional changes, stresses and plastic flow accompanying an allotropic transformation in one component of a fiber composite, taking into account the simultaneous stress relaxation which occurs.
Abstract: A theoretical analysis is made of the dimensional changes, stresses and plastic flow accompanying an allotropic transformation in one component of a fibre composite, taking into account the simultaneous stress relaxation which occurs. The theory predicts the transformation dimensional changes observed experimentally under various temperature cycling conditions and provides an estimate of the stresses. Extending the theory to include the effect of a variation in temperature, several categories of coefficients of thermal expansion are obtained, none of which correspond to the rule of mixtures. The predicted transition from one coefficient of expansion to another during continuous cooling is confirmed experimentally and the resulting dimensional changes verified.
32 citations
TL;DR: Comparison of stress relaxation and constant rate of strain data show that the cell walls of these algae exhibit non-linear viscoelastic behaviour and apparent changes in the quasi-static modulus with temperature can be explained satis factorily in terms of reaction rate theories for vis coelastic processes.
Abstract: Stress relaxation and constant rate of strain measurements were made on the cell walls of the green algae Nitella, Acetabularia, and Penicillus These plants have, as their main structural polysaccharide, cellulose, mannan, and xylan respectively The stress relaxation measurements were made in the temperature range o to 50 °C for the interval 0 02 to io3 s A limited number of constant rate of strain curves were also obtained for comparison with theoretical curves deduced from the relaxation data All three algae exhibit typical fibrous behaviour but Acetabularia could not be mechanically conditioned to give reproducible results The time-temperature correspondence of the data and its relevance to the molecular organization of the cell wall are discussed Structural changes with temperature, deduced in previous work from rigorous matching of the relaxation curves at different temperatures, are now thought not to occur The matching procedure only appears to work because the curves lack distinctive features on which to base the superposition Comparison of stress relaxation and constant rate of strain data show that the cell walls of these algae exhibit non-linear viscoelastic behaviour and apparent changes in the quasi-static modulus with temperature can be explained satis factorily in terms of reaction rate theories for viscoelastic processes
31 citations
TL;DR: In this article, the authors derived a simple formula for the time taken for the redistribution of stress in a structure subject to step loading, from an initial state to a final steady state to be practically complete.
Abstract: On the basis of some reasonable assumptions about the behaviour of structures in creep, a simple formula is derived for the time taken for the redistribution of stress in a structure, subject to step loading, from an initial state to a final steady state to be practically complete. The time taken is expressed in terms of the time taken for creep strain to become equal to a certain multiple of the elastic strain in a constant-stress creep test; this test is performed at a stress level which depends on the steady-state distribution of stress in the structure. The formula agrees remarkably well with numerical results in the literature, both for structures which are initially stress free and for structures with initial thermal stress. The formula seems to be well suited for practical use in engineering design.
30 citations
29 citations
TL;DR: In this article, the irradiation induced creep of polycrystalline graphites under constant tensile and compressive stresses in BR-2 is considered and it is shown that up to a fast neutron dose of 50 × 1020 n.cm−2 there is no large effect of irradiation temperature on creep strain between 300° and 650°C, and the increase in creep strain with dose at constant stress is similar in compression and tension up to 1 per cent.
TL;DR: In this article, the effects of sinusoidal internal stresses on average dislocation velocities are examined for the power law stress dependence, v = V 1 τ e m∗ ; the exponential stress dependence and the hyperbolic started that when the magnitude of the internal stresses is comparable with the applied stress, the stress dependence of the velocity becomes anomalously high.
TL;DR: In this paper, the authors applied the time-temperature superposition principle to yield stress, initial tangent moduli, and relaxation moduli data for all three types of loading.
Abstract: Epoxy–Versamid specimens were loaded in tension, compression, and flexure at different strain rates and temperatures to determine mode of failure, yield stress and strain, and tangent and relaxation moduli. Stress-strain curves were used to define brittle, ductile, ductile-rubbery, and rubbery modes of behavior which prevailed in different temperature-strain rate regions. The time-temperature superposition principle was applied to yield stress, initial tangent moduli, and relaxation moduli data for all three types of loading.
The transition regions, tangent and relaxation moduli, and shift factors were the same in tension, compression, and flexure. Thus the most convenient mode of loading can be used to determine the general time-temperature dependence. The ratio of compressive-to-tensile yield stress was almost constant over the entire ductile region. Flexural yielding data were used to predict yield stress in tension and compression, and stress relaxation master curves were shown to be related to elastic modulus vs. strain rate curves. The yielding phenomenon was interpreted using Eyring's theory of non-Newtonian viscoplastic flow. The apparent activation energy and activation volume were larger for tension than compression. A theory is offered to explain why yielding can occur in a cross-linked system.
TL;DR: In this article, the authors examined the plastic strain region from 3 × 10 −5 through macroscopic yielding in Ferrovac-E iron from room temperature to 77°K.
TL;DR: In this article, the significance of the log creep rate versus log stress plot is examined in detail for results on a Cr-Mo steel and it is shown how errors may readily arise in measurement of creep rates at very low stresses.
TL;DR: In this article, the elastic dipole distortion of stationary interstitial impurity atoms in lattice solution promotes nucleation and stabilization of double-kink-size screw dislocation segments on cross-slip planes.
Journal Article•
TL;DR: In this paper, the authors investigate the physical behavior of OSAKA MARINE CLAY under the stress relaxation test and show that for a given given increase in the strain, both the initial stress and the fully relaxed stress relaxations decrease with increasing temperature.
Abstract: THE MECHANICAL BEHAVIOR OF CLAY IS INVESTIGATED FROM THE THERMAL BEHAVIOR OF ITS ELASTICITY AND VISCOSITY. THE MECHANICAL BEHAVIOR OF THE CLAY SKELETON WHOSE STRESS AND STRAIN ARE EXPRESSED BY A LINEAR RELATION WITH A PARAMETER OF TIME HAS BEEN SIMULATED BY A MATHEMATICAL MODEL. VISCOSITY OF CLAY IS INFLUENCED BY TEMPERATURE AS SUGGESTED IN THE FLOW BEHAVIOR AT VARIOUS TEMPRATURES. THE EFFECT OF TEMPERATURE ON THE ELASTICITY OF CLAY CAN BE INVESTIGATED BY THE BEHAVIOR ON THE STRESS RELAXATION TESTS AT VARIOUS TEMPERATURES. THE EFFECT OF TEMPERATURE ON THE ELASTIC MODULI IN THE MODEL IS INVESTIGATED. RESULTS OF THE STRESS RELAXATION TESTS SHOW THAT FOR A GIVEN INCREMENT OF STRAIN BOTH THE INITIAL STRESS AND THE FULLY RELAXED STRESS RELAXATION DECREASES WITH INCREASING TEMPERATURE. THE BEHAVIOR OF OSAKA MARINE CLAY UNDER THE STRESS RELAXATION TEST IS WELL PREDICTED BY THE MECHANICAL MODEL. ELASTIC MODULI DECREASE WITH THE INCREASE IN TEMPERATURE.
TL;DR: In this article, a model consisting of an isolated spring in parallel with a spring and dashpot in series was used as an aid in the derivation of equations describing stress relaxation.
Abstract: Stress relaxation tests were performed with six tropical American species. Stress relaxation was not found to be a linear function of strain at any level of strain. At qual low levels of strain, stress relaxation in compression was much greater than in tension. A mechanical model consisting of an isolated spring in parallel with a spring and dashpot in series was used as an aid in the derivation of equations describing stress relaxation. An attempt to apply Newtonian viscous theory to the model was unsuccessful in accounting for rate of relaxation. However, when the hyperbolic sine law of viscous flow was applied, mathematically derived curves fitted the data very well. Stress relaxation appears to be related to “departure strain” which may be obtained readily from static stress strain diagrams.
TL;DR: In this article, the mechanical and rheo-optical properties of a styrene-butadiene-styrene block copolymer of a given chemical composition are dependent upon the morphology of the polymer as affected by the solvent system from which a polymer film is cast.
Abstract: : The mechanical and rheo-optical properties of a styrene-butadiene-styrene block copolymer of a given chemical composition are dependent upon the morphology of the polymer as affected by the solvent system from which a polymer film is cast. Films cast from methyl ethyl ketone and from toluene are compared. Properties found to differ are the stress-strain curve, the birefringence-strain curve, stress relaxation, birefringence relaxation and the dynamic mechanical spectra. (Author)
Patent•
27 Jun 1969TL;DR: In this paper, the authors measured the soil creep rate in situ by lowering a shear testing device into a bore hole and expanding it so that opposing pressure surfaces of the device engage facing surface of the bore hole with a constant normal pressure.
Abstract: Soil creep rate is measured in situ by lowering a shear testing device into a bore hole and expanding it so that opposing pressure surfaces of the device engage facing surfaces of the bore hole with a constant normal pressure. A force less than that which would exceed the soil shearing strength under the applied normal pressure is then exerted on the device axially of the bore hole to induce a predetermined and constant shearing stress in the soil. A record is made of the deformation of the soil as a function of time for different shearing stresses to generate a family of characteristic deformation curves. The first derivative of each curve with respect to time is the shear rate, which tends to decrease to a substantially constant value with increasing time. This constant shear rate is referred to as the creep rate. A plot of the creep rate against shearing stress yields an empirical value for the creep threshold stress; and a plot of different creep threshold stresses for different values of normal stress defines a stable zone in the shearing stress-normal stress plot.
TL;DR: In this article, a 5 MHz ultrasonic transducer transmission method was used to study recovery processes subsequent to plastic deformation in a polycrystalline, high purity iron-0.05% carbon alloy.
01 May 1969
TL;DR: In this paper, the authors investigated the effect of three-dimensional COMPRESSIVE STRESS systems on the CREEP of CONCRETE under varying three different stress levels for a period of two years.
Abstract: RESULTS ARE GIVEN FOR THE CREEP OF CONCRETE UNDER VARIOUS THREE DIMENSIONAL COMPRESSIVE STRESS SYSTEMS AT TWO TEMPERATURES FOR A LOADING PERIOD OF 2 YEARS. THE EXISTENCE OF A CREEP POISSON'S RATION OF A SIMILAR MAGNITUDE TO THE ELASTIC POISSON'S RATIO HAS BEEN CONFIRMED AND A SIMPLE FORMULA IS GIVEN FOR THE PREDICTION OF CREEP UNDER MULTIAXIAL STRESS SYSTEMS FROM THE MORE EASILY OBTAINED UNIAXIAL CREEP CURVES. CREEP RECOVERY AFTER THE REMOVAL OF THREE-DIMENSIONAL STRESS SYSTEMS IS SHOWN TO BEAR NO DIRECT RELATION TO EITHER MEASURED ELASTIC STRAIN REVOVERY OR MEASURED CREEP MAGNITUDE. /AUTHOR/
TL;DR: In this paper, the tension transducer or a modification of it has the capability of measuring cord forces in tires of different constructions and cord materials under diverse loading situations, and has approximately 2.6 times the output of the smaller transducers used in this investigation.
Abstract: with one gage in each leg of a Wheatstone bridge. This setup provides lead-wire temperature compensation, eliminates the effect of undesirable bending, and has approximately 2.6 times the output of the smaller transducer used in this investigation. Although all data reported here were obtained from 8.25-14 two-ply rayon tires, the tension transducer or a modification of it has 'the capability of measuring cord forces in tires of different constructions and cord materials under diverse loading situations.
TL;DR: In this article, the variation of stress and strain in metals as they are subjected to shock impulses of up to 200 kb and released is presented. But the results of these measurements are not consistent with a simple elasto-plastic model for metal behaviour.
Abstract: Measurements are presented of the variation of stress and strain in metals as they are subjected to shock impulses of up to 200 kb and released. Results have been obtained for a magnesium alloy and for two grades of aluminium of very different yield strengths. The release characteristics of these metals are shown to be broadly consistent with a simple elasto-plastic model for metal behaviour. Elasto-plastic Hugoniots are fitted to published shock data for the metals used; a revised calibration is given for the manganin stress transducer employed, and a new method of construction is illustrated. Stress relaxation is observed in magnesium and is associated with the easy slip on the basal plane in hexagonal close-packed materials.
TL;DR: Tension stress and shearing strain vs time for simultaneous stress relaxation and creep in polyurethane was studied in this paper, where the authors compared tension stress, shearing, and stress relaxation.
Abstract: Tension stress and shearing strain vs time for simultaneous stress relaxation and creep in polyurethane
TL;DR: In this paper, an expression for strain relaxation is derived from the transition state theory for the asymmetrical forms of the energy barrier, which is in full agreement with the dislocation velocity measurements.